Currently, oil resources are heading to the direction of heavy, low-grade oils, and heavy oil has become an important feedstock for refineries all over the world. Heavy oil can be separated into mixtures of different types of hydrocarbons according to polarity, respectively, saturates, aromatics, resins and asphaltenes. The saturates, the aromatics and the resins can be converted to end products, e.g. light vehicle fuels such as gasoline and gas oil, and chemical raw materials such as ethylene and propylene, by using conventional techniques for the conversion of heavy oil to light fractions; while asphaltenes not only cannot be converted to end products efficiently, but also have an extremely detrimental impact on processing procedures.
In practical industrial production, the coke, which is byproducts of the delayed coking process and catalytic cracking process, mainly comes from asphaltenes, in particular, when the content of asphaltenes in the raw materials to be processed is too high, not only the yield of coke is significantly increased, but also the yield of light oil product is decreased, and in worse scenarios, the delayed coking process and catalytic cracking process cannot even be used to process the feedstocks. Taking the delayed coking process as an example, when the content of asphaltenes in the raw materials is too high, the heating furnace radiant tube tends to be coked severely, resulting in the device unable to be operated normally, and in worse scenarios, the shot coke can be easily formed, jeopardizing the safety of production. During a heavy oil hydrotreating process, the asphaltene is most difficult to be converted, not only affecting the yield of catalytic cracking light oil, but also easily causing carbon deposition on surface of the hydrotreating catalyst so as to decrease its activity, also resulting in a short operating cycle for the hydrotreating device, and greatly affecting the overall operation and economic benefit of refineries.
It can be seen from technical solutions for the conversion of heavy oil to light fractions which are employed in current refining industries that, a route with an early stage solvent deasphalting process is a feasible route to process heavy oil with high level of asphaltenes, that is, removing resins and asphaltenes from heavy oil by using a physical method of solvent extraction processing firstly, obtaining de-asphalted oil with low heavy metal content and carbon residue value, then the de-asphalted oil is treated as a catalytic cracking or hydrocracking feedstock and converted to light fractions; after being blended with vacuum residual oil, asphaltene-rich de-oiled residues can be introduced into the delayed coking device to be processed, however, in order to prevent severely coking of the heating furnace radiant tube of the delayed coking device due to high asphaltenes, the blending ratio of de-oiled residues is very limited; moreover, after the de-oiled residues are introduced into the delayed coking device, most of them are transformed into coke and gases, and their conversion ratio to light oil products is also low, and economic benefits are poor. Therefore, currently, there is no highly-efficient method for the conversion of asphaltene-rich de-oiled residues to light fractions.